Actin Regulatory Proteins

Question 1

Functions of Arp complex (in actin filament regulation)

Answer 1

1. Branching (at 70 degrees)
2. Nucleation
3. Capping (at the minus end)

Question 2

Functions of ADF/Cofilin

Answer 2

1. Sequestering (but does not inhibit polymerisation)

2. Severing actin filaments (to increase the number of plus ends and increase rate of polymerisation)

Question 3

Functions of severin

Answer 3

1. Severing

2. Capping the plus ends

Question 4

Functions of gelsolin

Answer 4

1. Severing

2. Capping the plus ends

Question 5

Function of a-actinin

Answer 5

1. Bundling of actin filaments (loose bundling to allow for binding of myosin proteins)

Question 6

Function of fimbrin

Answer 6

1. Bundling of actin filaments (Parallel and tight bundles, preventing binding of other proteins like myosin)

Question 7

Proteins involved in capping

Answer 7

Capping at plus ends: Gelsolin, Severin, Cap Z

Capping at minus ends: Arp2/3 complex, Tropomodulin

Question 8

Proteins involved in membrane connections with the ECM

Answer 8

a-catenin
Talin
spectrin
ERM (erzin/radixin/moesin)

Question 9

Gel-sol transition is brought about by ______ proteins.

Answer 9

Severing proteins

Gelsolin, severin, ADF/cofilin

Question 10

Which two actin proteins are regulated/affected by intracellular calcium ions level?

Answer 10

1. Gelsolin
   - Ca2+ dependent severing
2. a-actinin
   - Binding decreases at high Ca2+

Question 11

Function of profilin

Answer 11

Sequesters actin monomers

Question 12

Activating Cdc42 (Ras G protein) will lead to _________ formation.

Answer 12

filopodia

Polarised motility, actin polymerisation

Question 13

Activating Rac (Ras G protein) will lead to _________ formation.

Answer 13

Lamellipodia

Focal adhesion and actin polymerisation assembly at the leading edge

Question 14

Activating Rho (Ras G protein) will lead to _______ formation.

Answer 14

stress fiber (generation of tension and contraction - cortex under tension)

Question 15

The 3 actin proteins that are regulated by IP3 binding are:

Answer 15

1. ADF/cofilin (sequestering)
2. Profilin (sequestering)
3. Gelsolin (capping at plus ends)